1. Field of the Invention
This invention relates, generally, to cleaning the drums of ready mixed concrete trucks. More particularly, it relates to a control system for operating an apparatus that performs such cleaning.
2. Description of the Prior Art
U.S. Pat. No. 7,546,843 discloses a machine or apparatus that uses water under pressure to blast green or hardened concrete from the inside of a drum of a ready mixed concrete truck. That patent is incorporated herein by reference. The machine disclosed in that patent uses a moderate horsepower engine because it positions the water-emitting nozzle in very close proximity to the concrete being removed by following the peaks and valleys of the mixer drum. This distinguishes it from earlier machines that use high pressure water and high flow thus high horsepower engines because they position the nozzle on the axis of rotation of the drum and have no means for positioning the nozzle closer to the concrete.
A bell crank is used to oscillate the nozzle in the patented invention. The bell crank can be mechanically adjusted to change the angle of sweep of the nozzle but such adjustment is time-consuming.
Thus there is a need for an improved method of changing the angle of sweep of the nozzle.
The oscillating nozzle is mounted to the leading end of an elongate boom. The rate of elongate boom extension into the interior of the drum and retraction from said interior is controlled by an operator who visually observes the rate of extension and retraction by observing the rate of rotation of a circular disk mounted on the machine and increases or decreases such rate using an analog control system.
Thus there is a need for an improved control system that enables an operator to control the extension and retraction rates of the elongate boom by digital means so that the rotating disk and analog control system are not needed.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how the needed improvements could be provided.